Can you use sub queries with phql?

This piece of working sql gives me the position of an item in the subquery:

SELECT x.position
FROM
(SELECT ftp.topic_id, ftp.id as id, @rownum := @rownum + 1 AS position
 FROM forum_topic_post ftp
 JOIN (SELECT @rownum := 0) r
 where ftp.topic_id = 11134
 ORDER BY ftp.id ASC) as x
where x.id = 310781

Is it possible now to transpose this into phql as previous reading has told me this is not possible.